Arc lamp with sapphire sleeve



May 2, 1961 R. HElNE-GELDERN ARC LAMP WITH SAPPHIRE SLEEVE Filed Oct. 2, 1959 FIG ROBERT HElNE-GELDERN ATTORN EYS United States Patent O 2,982,877 ARC LAMP WITH SAPPHIRE SLEEVE Robert Heine-Geldem, Upper Montclair, N J., assignor to Engelhard Hanovia, Inc., a corporation of New Jersey Filed Oct. 2, 1959, Ser. No. 844,078

8 Claims. (Cl. S13-'184) This invention relates to arc lamps and more particularly to high pressure and high power arc discharge lamps.

In the eld of arc discharge lamps of the high pressure and high power type, there has been considerable difficulty in the devitrication of the quartz tubes which are employed as envelopes. In the capillary type tubes, where the arc is confined by a narrow passageway, this effect has caused arc lamp failures, by devitrification, particularly in the immediate vicinity of the electrodes, where most of theV power dissipation occurs.

It has been proposed heretofore to use sapphire tubing in place of the quartz envelopes, with metal tubes connected to the sapphire sleeve at each end. While this is satisfactory at relatively low pressures and power levels, it is wholly unsatisfactory at the normal capillary arc lamp pressures and powers. Typical operating pressures of capillary lamps are 30 to 50 atmospheres, while the the metal-to-sapphire seal fails because of the dilerenceY in the temperature coefficient of expansion of the sapphire and metal and the poor sealing properties of sapphire material. v

Accordingly, a principal object of the present invention is -to increase the life of capillary arc lamps of the high pressure and high power type.

In accordance with the present invention, the foregoing object is achieved by the use of a sapphire liner within a quartz envelope. Each of the electrodes may be enclosed by the cylindrical sapphire liner, and this liner may provide the capillary channel Vextending fromV one electrode to the other. In one illustrative embodiment, the sapphire sleeve makes a slip t within the enclosing quartz envelope and there is no need to make any seals to the sapphire sleeve.

This arrangement has the advantage of providing heat resistant sapphire material at the critical areas adjacent the electrodes, without the disadvantage of sapphire-tometal seals which have produced arc lamp failures in the past.

In accordance with a feature of the invention, a capillary type arc lamp is provided with an outer sealed envelope and an inner cylindrical sapphire sleeve closely enclosing both electrodes and providing a capillary channel between the electrodes. The sapphire sleeve is mounted for free thermal expansion and contraction wholly vwithin the envelope of the lamp and forms no part of the sealed envelope. Gas under an operating pressure from 1K0 to 20 up to 50 or more atmospheres is provided within the envelope of the tube.

Other objects, features and advantages of the invention will become apparent .from a consideration of the following detailed description, from the claims and from the drawings, in which:

Figure 1 represents a capillary arc lamp of the high 2,982,877 v Patented May 2, 1961 Figure 2 is an enlarged cross-sectional View along lines 2-2 of Figure l.

Referring to the drawings, Figure l shows a gas discharge tube having an outer quartz envelope 12 and an inner sapphire sleeve 14, in accordance with the inven-` tion. The two electrodes 16 and 18 extend into the ends of the sapphire sleeve 14. The opening through the stapphire sleeve forms the confining capillary in which the arc. discharge between terminals 16 and 18 occurs. The sapphire sleeve 14 makes a slip lit with the enclosing quartz tube 12. It is somewhat loosely mounted Within the quartz envelope so that it may freely expand or contract with changes in temperature. No seals are required between the sapphire sleeve 14 and any other elements of the gas discharge lamp. With regard to the properties of quartz and sapphire, both are transparent refractory materials, and the sapphire'material has a melting point which is several hundred degrees higher than the quartz.

The connections between the cylindrical molybdenumv noted that the cylindrical terminal 20 and the cylindricall electrode 16 are cut away in the areas 31 through34 to form relatively flat surfaces for the securing of the tube lead-in foils 24. The fused quartz envelope forms a seal around and between the two foils 24 which interconnect terminal 20 and electrode'16. Other known techniques for providing connections to the inner electrodes, which are capable of handling high levels of power, may also be employed. v

In capillary type arc larnps which have been used heretofore, the walls of the capillary opening are of quartz material. When quartz is employed, the high temperatures and thermal shock in the region 36 adjacent the electrode as shown in Figure 2 have tended to produce devitrification and failure of the quartz material. VWhen the sapphire sleeve 14 is used, however, this adverse ef` fect is largely eliminated, and the life of the capillary are lamp is greatly extended.

Returing to FigureY 1,'the power supply 38 is shown connected to the terminals 20-and 22. In a typicalcapillary tube application, xenon gas may be employed at an operating pressure of from 30 to 50 atmospheres and at a cold pressure of from 8 to 12 atmospheres. The power supplied to the tube may be about 1,000 watts per inch. Under these conditions and using a known type of radio frequency starter, the power supply 38 would provide power at a voltage of about 500 volts to the combination of the ballast and the tube. With different electrode spacings and other varia-tions in conditions, higher 0r lower voltages are required.

In a typical capillary arc lamp having a one inch spacing between the electrodes 16 and 18, approximately 1,200 watts of power were applied to the'lamp. With regard to the use of the terms high pressure and high power in the present specification and claims, operating pressures `greater than l0 atmospheres and powers above 300 watts per inch are considered to be high.

In capillary type arc lamps, the internal diameter of the capillary may range from about one millimeter up to 8 or l0 millimeters, for example. In the pres'ent case, the sapphire sleeve 14 has a capillary with an internal diameter of two millimeters, and the wall thickness of the sapphire sleeve is also two millimeters.' The thickness of the quartz envelope is also about two millimeters, so the outer diameter of the quartz envelope 12 is approxi- Other gases than xenon may, of course, be employed. In

this'regard, argon, krypton, helium and mercuryshould specifically be included. When mercury is used, it'is normal practice to employ, in addition, a starting 'gasy such as argon or Xenon. Y

The outer envelope is preferably of silica, either in the formof fused quartz or high silica glass. It is contemplated, however, that other envelope materials which are transparent to radiations from the enclosed gas may be employed under appropriate circumstances.

It is again noted that the principal advantage of the present invention accrues from the use of a sapphire sleeve which is mounted for free thermal expansion and contraction, and which is used with the arc lamp electrodes mounted Within its inner passageway. When a high pressure, high power arc lamp is provided with a sapphire sleeve in this structural arrangement, its life is greatly extended. t.

It is to be understood that the above des'cribed arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is: Y

l. A capillary arc lamp comprising an outer silica envelope, a sapphire sleeve mounted for free thermal expansion and contraction within said envelope, a pair of electrodes mounted within the ends of said sapphire sleeve, the opening through said sleeve forming a capillary for confining the arc discharge between said electrodes, gas in said envelope having an operating pressure greater than 10 atmospheres, and power supply means for applying power to said electrodes at a level of more than 300 watts per inch of distance between s'aid electrodes.

2. A capillary arc lamp comprising an outer envelope, a sapphire sleeve mounted for free thermal expansion and contraction within said envelope, a pair of electrodes mounted within the ends of said sapphire sleeve, the opening through said sleeve forming'a capillary for conlining the arcrdischarge between said electrodes, gas in said envelope having an operating pressure of about 30- 5 0 atmospheres, and power supply means for applying power to said electrodes at a level of more than 500 watts per inch of space between said electrodes.

3. A capillary arc lamp comprising an outer silica envelope, a sapphire sleeve mounted for free thermal '4 expansion and contraction wholly within said envelope, and a pair of electrodes mounted within the ends of said sapphire sleeve, with the periphery of the electrodes being immediately adjacent the inner surface of said sleeve. 4. A capillary arc lamp comprising an outer silica envelope, a sapphire sleeve mounted for free thermal expansion and contraction within said envelope, a pair of electrodes mounted within the ends of said .sapphire sleeve, the opening through said sleeve forming a'capillary for conining the arc discharge'between said electrodes, gas in said envelope having an operating pressure greater than 30 atmospheres, and power supply means for applying power to said electrodes at a level of about 1000 watts or more per inch of distance between said electrodes.

5. A capillary arc lamp comprising an outer silica envelope, a sapphire sleeve mounted for free thermal eX- pansion and contraction-within said envelope, a pair of electrodes mounted within the ends of saidk sapphire sleeve, the opening through said sleeve forming a capillary for confining the arc discharge between said electrodes, and gas in said envelope having an operating pressure greater than 30 atmospheres, and means fork applying a high level of powei to said electrodes.

6. A capillary arc lamp comprising an outer envelope,

a sapphire sleeve mounted for free thermal expansion and contraction wholly within said envelope, and a pair of electrodes mounted within the ends of said sapphirel sleeve, with the periphery of the electrodes being in immediate proximity to the inner surface of said isleeve, and gas in said envelope having an operating pressure greater than 10 atmospheres.

7. A capillary arc lamp comprising an outer envelope, a sapphire sleeve mounted for free thermal expansion and contraction wholly within said envelope, and a pair of electrodes mounted within the ends of said sapphire References Cited in the le of this patent UNITED STATES PATENTS 2,367,595 Marden Jan. 16, 1945 Gaidies et al. Aug. 7, 1934 

